Electrical wave transmission



June 146A, 1925.

M. l. PUPIN ELECTRICAL WAVE TRANSMISSION Aorigina Filed Dec. 11, zvsneets-sheet 1 @IAN 10N la! .QN N NN l. .E am L.. 1 AISI? IMI JI .Q /f kas@ W//m weg 1/ Q `)une 16, 1925.

M. l. PUPIN ELECTRICAL WVE TRANSMISSION Original Filed Deo. l1, 1915 2 Sheets-Sheet 2 Patented .lune 16, 1925.

UNITED STATES PATENT OFFICE.

MICHAEL I. PUPIN, OF NORFOLK, CONNECTICUT, ASSIGNOR TO WESTINGHOUSE ELEC- TRIC AND MANUFACTURING COMPANY, F EAST PITTSBURGH, PENNSYLVANIA, A

CORPORATION 0F PENNSYLVANIA.

ELECTRICAL WAVE TRANSMISSION.

Application led December 11, 1915, Serial No. 430,995. Renewed December 15, 1920.

To all whom it may 'comer/n:

Be it known that I, MTCHAEL I. PUPIN,`

' structed sectional wave conductors (called here the pilot wave conductors) between the wave conductor which receives the electrical wave energy and the local translating devices which are to be actuated by this miergy. The object of the invention is to exclude from the circuits containing the translating devices all electrical waves which are not intended for them.

Referring to the diagrams of the. drawings which form a part of this specification; Figure 1 is a diagram of a sectional wave conductor consisting of ap roximately equal indnctance coils shunted sy approximately equal condensers;

Fig. 9. is a diagram representing a sectional wave conductor interposed between a wireless receiving antenna and the circuits containing local translating devices.

Fig. 3 is a diagraml representing a sectional wave conductor of a different type from that in Fig. 1 and Fig. 2, irfterposed between the system of conductors represented in Fig. Q'and the local receiving devices. Fig. 4 is a third type of sectional wave conductor.

2 cosh Zbg-B2-1LJ Let L :SX henrys (3:2)(10's farads R:170. ohms at x10 periods:r,+r. where pgs-Ba? Fig. 5 is a diagram representing by curves the relation between the attenuation power and frequency in the sectional wave conductors of Fig. 2 and of Fig. 3, and the same relation when the eilects of these two sectional wave conductors are combined.

Referring t0 Fig. 1, the elements 1, 2, 3, 4, 5, are `inductance coils connected in series. They should preferably be approximately equal. Condensers 6, 7, 8, 9, 10, 11, are connected in parallel with the inductance coils; they shouldk also be approximately equal to each other. Assume that there are five coils and six condensers. They forni a sectional wave conductor of five sections and having characteristics which will be now discussed.

The theory of the electrical motion in sectional wave conductors was first published by the applicant in 1899 in the Transactions of the American Institute of Electrical Engineers, Vol. XVI, pp 91-142, to which reference is made for the mathematical theory underlying this` invention. Reference should also be made to the applicants publication in Vol. XVII of the same transactions, pages 445-507.

Let Lzzinductance in henrys of each coil Czcapacity in i'arads of each condenser liz-.resistance associated with each coil 'lhen if b and a denote the attenuation constant and the wave length constant per section, we shall have :2 cosh b cos L -:Q-pgLCz-A 2 sinh b sin azpCRL- B where n cosh b:1(e"-{eb), sinh b:1/2(c"-e") From these the following formula'follows:

The shortest natural period of the sectional wave conductor is that of one of its sec-v and act like a very high frequency tions, which is approximately 2 m SeCOIldS.

where f is any frequency: *mdf Si 1 Giving n successlvely the value l, a,

3, the values of b and of 5b (the attenuation power) for various frequencies was obtained. In Fig. 5 a graphical representation is given of the relation between 5b and the frequency. The attenuation factor for theK frequency for which 5b has been calculated is eb, that is to say, a wave of amplitude I at the beginning of the sectional wave conductor will have an amplitude equal to Ie'5b at the end. It is easily seen from the curve in Fig. 5 that if 25 103 p. p. s. is the signalling frequency, then all frequencies appreciably higher than the signalling frequency will be rapidly attenuated. The frequencies below the signalling frequency will be transmitted very well.

In other words, this pilot conductor has a sufficiently large number of sections per wave lengthl for frequencies lower than the signalling frequency, but for frequencies higher than the signalling frequency the number of sections per wave length becomes small. This structural characteristic in sectional conductors of this type gives the attenuation power characteristic represented by curve A in Fig. 5.

In wireless telegraphy and telephony much interference is experienced from the induction effects produced in the receiving antenna by the action of electrica-l' discharges in the atmosphere. These discharges are called strays, atmospherics, or statics. It is a. well established fact that a large part of these discharges are very short pulses simple harmonic electromotive force of very high l damping. Their frequency is much higher than 25 103 p. p. s., which is the signalling frequency usually adopted for long distance wireless telegraph work. A wireless Receiving station in which a sectional wave conductor just described is employed as a pilot wave conductor, that is for connecting the antenna to the local circuits, containing the translating devices, w-ill be screened against these high frequency electrical disturbances. Such an arrangement is shown in the diagram of Fig. 2.

In this diagram, an antenna 17, 18, 19,

20, grounded at 17, is connected to the pilot wave conductor 21, 22, 23, 31. The pilot wave conductor is connected to a re* peater which is here represented syn1bolically by the well known vacuum tube having a hot cathode 12, a cold anode 13, and a third electrode 14, the so-called grid. The apparatus to be actuated by the electronictive force generated by the energizing circuit 13, 15, 12, is connected to the secondary winding 15, 16.

The protection against disturbing electricaldischarges in the atmosphere which the sectional wave conductor just described gives to the circuits containing the translat ing devices can be further increased as follows: A high frequency electrical pulse cannot be transmitted directly along the scctional wave conductor represented in Fig. 2. but a part of its action will be transmitted indirectly. The action of the pulse will store up some energy in those parts of the pilot wave conductor which are nearest to the antenna, and in these energized parts free oscillations will be started which are easily transmitted to the circuits containing local translating devices, because these oscillations are of low frequency. In the case described here the highest frequency of the free oscillations is about 18,000 p. p. and, as is shown in the curve A of Fig. 5, such a frequency is transmitted very elliciently overA the pilot conductor just described. These free oscillations of low frequency should in the first place have a large decrement as is provided here by giving each section as large a resistance as is eon'ipatible with otherl considerations; in the second place they should be excluded from the local translating devices by another pilot conductor which transmits the signalling frequency satisfacv torily but attenuates very rapidly lower frequencies. This second pilot conductor is an artificial cable which has at equal intervals in parallel arrangement suitable inductance coils and condensers connected in series.

Referring to Fig. 3, there is represented in this diagram, a sectional wave conductor consisting of, say, 1l pairs of approximately equal resistances 39, 40, 52. Bridged across these are capacities Gl, (52, 623, 7l in series with equal induetances T5, T6, 88. The capacities are graded in value in accordance with a rule which will be explained presently.

Let the inductance ol each coil be LIOXIO henrys, and let its efl'eclive resistance R be very small in comparison with the react-ance, say

where Let the resistance R, of each resistance unit ybe R,::50 ohms and the capacity C of each condenser be where 1 L* *L (l P2110) so that near thevalues of p which satisfy the resonance condition, namely pzLCzl, the attenuation constant would be enormous. For other values of vp this constant would be small. Thatis to say, this pilot conductor would attenuate a very narrow interval of frequencies. This interval is widened very much by giving to the condensers 61, 62, 63 74, gradually increasing values as follows:

Capacity of condenser 61 is 4)(10 farads Ca acity of condenser 62 is 4.28)(10" fara s Capacity of condenser 63 is 4.58)(10-s farads etc., that is, each capacity is about 7 er cent higher than the preceding one, so` t at the last capacity is about 9.63)(10" farads. In this case the ilot conductor will attenuate very strong yl a frequency interval of 40 per cent. below a given frequency. With the values given above for the constants L` and C, this interval will be between about 12.5 10a p. p. s and 18x10 p. p. s. and the attenuation power will be as indicated by the curve B of Fig. 5. But this is the interval of frequencies within which are located all the free periods of the first ductor, and since these freey oscil ations of the first pilot cqnductor carry all the energy of the static it is clear that the second pilot conductor will dissipate it. This dissi ation of the energy conveyed by the 'l ree oscillations of the first ilot conductor is carried out in practice v y connectin the pilot conductor of Fig. 8 1n series witv the energizing circuit 16 of Fig. 2, rgiving a curve of attenuation power with respect to frequency as C in Fig. 5. Connected with the second pilot wave conductor is a system of conductors containin the translating devices. Thus in Fig. 3 1s represented ay resistance compensator connected to the second pilot wave conductor by the transformer 93, 94 leading to a resistance compensator of the vacuum tube type, described 1n application Serial No. 51,151 filed on September 17, 1915 now patent No. ,1,334,-

ilot .con-

If the capacities were all equal and each equal to 4)(10's farads, then the attenuation constant b of the sectional wave conductor would be given by the following formula:

165 dated March 16, 1920, by the applicant and E. H. Armstrong.

In place of the pilot wave conductor of the second type, just described, a thirdtype of pilot wave conductor may be employed which also attenuates effectivel frequencies below a given frequency. This third t pe of pilot wave conductor is'represented iagrammatically in Fig. 4. This is the well known artificial cable consisting of a suitable numberof equal resistances 101, 102, 103, 108 and equal condensers 109, 110, 111, 112, 113,- paralleled by equal inductances 114, 115,116, 117, Let each resistance u nit have a resistance equal to 200 ohms, each condenser have acapacity of 2 10rs farads, and let each inductance be equal to 2 1(r3 henrys, then the wave conductor will transmit well frequencies in the vicinity of 25)(,103 p. p. s. but will attenuate ra idl ticular y t ose below 15 103 p. p. s. The mathematical theory for all these and similar wave conductors can be obtained easily by followin the mathematical method described by t ve author inthe' references cited above.

The broad invention consists-in preventing all but a 'narrow range of frequencies all low frequencies and par-- ing suitable pilot wave conductors between i these circuits and the conductors receiving the signalling wave energy, and I have described several of the vbest types of such pilot wave conductors, but I do not limit myself to these types.

In the practice. of this invention it is not permissible to tunethe antenna to the signallin frequency. If tuning 'is to be employe then the antenna should vbe tuned to a frequenc different from the si nalling frequency yan preferabl tuned to t e highest natural frequency o the first pilot conductor so that thel antenna and the first pilot conductor have one natural'frequency in common which will be dissipated by the second 'pilot conductor.

lclaim:

1. A .wave receiving station having a receiving conductor and a local translating device, between which is interposed a twopart sectional wave conductor, onepart of which has a large attenuation power for v sectional wave conductor having natural periods of oscillation of a frequency substantially. less than the frequency of the waves to be received, the other part of the sectional wave conductor having a high attenuation power for low. frequency waves including those resulting from the natural oscillations of the first part of the sectional wave conductor, the receiving conductor having a natural period of oscillation approximately corresponding to one natural period of oscillation of the first part of the sectional wave conductor.

9.. A wave receiving station having a receiving conductor and a local translating device, between which is interposed a twopart sectional wave conductor, one part of which has a large attenuation power for wave frequencies substantially higher than the frequency of the waves to be received, the sectional elements of that part of the sectional wave conductor having natural periods of oscillation of a frequency substantially less thanthe frequency of the waves to be received, the other part of lthe sectional wave conductor having a high attenuation power for low frequency waves including thoseX resulting from the natural oscillations of the first part of the sectional wave conductor, the receiving conductor having a natural period of oscillation corresponding to the highest natural period of osllation of the first part of the sectional wave conductor.

3. A receiving station for radio frequency waves having a receiving conductor and a local translating device, between which is interposed a two-part sectional wave conductor, one part of which has a large attenuation power for wave frequencies substantially higher than the radio frequency of the waves to be received, the sectional elements of that part of the sectional wave conductor having natural periods of vibration of a frequency substantially less than the frequency of the waves to be received, the other part of the sectional wave conductor having a high attenuation power for low frequency waves including those resulting from the natural oscillations of the iirst part of the sectional wave conductor.

Ll. A wave receiving station having a receiving conductor and a local translating device, between which is interposed a twopart sectional wave conductor, one part of which has a large attenuation power for wave frequencies substantially higher than the frequency of the waves to be received, the sectional elements of that part of the sectional wave conductor having natural periods of vibration of a frequency substantially less than the frequency of the waves to be received, the other part of the sectional wave conductor having a large attenuation power for low frequency waves and being made upof sectional elements having natural periods of oscillation which differ from one another by ,small increments throughout a considerable range which includes the natural periods of oscillation of .higher frequency than the waves of radio frequency to be conducted, whereby the attenuation power for waves of such frequency is high, and the individual elements of the series having natural periods of oscillation substantially less than the frequency of the waves to be conducted; the second series of wave conductor elements having' a large attenuation power for low frequency waves including those resulting from the natural oscillations of the iii-st series of wave conductor elements.

t3. A wave conductor selective with respect to a narrow rance of frequencies comprising two series o sectional wave conductor elements, the number of elements oi' the first series being small per wave length of waves of substantially higher freqnenr)y than the waves to be conducted, whereby the attenuation power for waves of such frequency is high, and the individual elements of the, series having natural periods` o t' oscillation substantially less than the frequency of the waves to be conducted; the

second series of wave conductor elements having a large attenuation power for low frequency waves and having individually natural periods of oscillation which differ from one another by small increments. throughout a considerable range, which includes the natural periods of oscillation ot' the lirst series of wave conductor elements.

7. A receiving system for discriminating between periodic sustained energy of a given frequency and disturbing energy, comprising a receiving conductor tuned to a frequency different from said given frequency, a translating device and a network connecting said conductor to said device. said network comprising a band filter for transmitting energy of a band ot' frequencies including said given frequency, and excluding the frequencies of all the natural oscillations of said network.

8. ln a radio receiving system, an indicating instrument, a recurrent network ot similar sections, said network containing damping resistance in each, section, and means for transferring received energy to said indicating instrument through said network.

9. The combination at a signal station of i in llU

a signal circuit and an electric wave filter connected thereto, said filter comprising a plurality of recurring sections each of said sections com rising lumped resistance, lumped capaclty and lumped inductance, said resistance, capacity and inductance having values depending upon the frequencv of the impulses to be transmitted through said filter.

10. In a signaling system the combination of a detuned antenna, a frequency selective amplifying means associated therewith, and means including a band filter all the natural oscillation frequencies of which are outside the frequency transmission band of said filter associated with said amplifier for translating the signals.

11. A receiving system comprising a receiving conductor, a translating device and means including a wave filter connecting said receiving conductor to said device, said l filter having a transmission range includmg a band of frequencies and excluding su stantially all frequencies outside said band and having no natural oscillation frequency within said band.

12. The method of receivin Asignals free from static interference, whic selectively receiving signals in accordance with the frequency of forced oscillations and in damping free oscillations, for iving the frequency thereof a value di erent from that of the signal oscillations to be received.

13. The method of signal reception, which consists in damping the received oscillations for giving the frequency of free oscillations a value different from that of the signal oscillations to be received, amplifying the signal oscillations, and in selectively receiving the amplified signal oscillations to the exclusion of the different frequency free oscillations.

consists in' means for transferring energy from said 16. The method of receiving signalswhich comprises converting substantial y all of the static energy received therewith into oscillations differing in frequency from that of said signals without changing thefrequency of the received signal energy and selectlng out the oscillations of the frequency of the received si al Wave from said converted energy o different frequency.

17. A system for selectively transmitting periodic energy of a given frequency to the substantial exclusion of other energy, comprising a plurality of energy transfer devices arranged in tandem, each of said devices being highly damped and havin its stiffness and inertia factors so vrela as to make said device most strongly responsive tov periodic energy of the given frequency.

18. Means for eliminating the effectA of disturbances upon transmission lines comprising means for imparting to `substantially all of the disturbing energy a characteristic differing from that of the energy to be transmitted, and means for selectively transmitting to a translating device the energy to be transmitted, to the substantial exclusion of said disturbing energy of different characteristic.

19. A transmission system comprisin a unidirectionally conducting element an a second unidirectionally conducting element and a band filter between said unidirectionally conducting elements, said band filter' ture.

MICHAEL I. PUPIN. 

